The invention relates to a multi fiber optical ferrule, a tool for forming the multi fiber optical ferrule and a method of making the multi fiber optical ferrule.
The demands placed on local area networks and wide area networks require an ever-increasing capability to handle more data flowing at faster data rates. Optical networks utilizing optical communication equipment are utilized to address this need. Such optical networks include optical switches having greater numbers of lines in and out in order to accommodate the increased data traffic. For example, current optical switches may have an input/output relationship as little as 512 by 512 and may be expanded to be greater than 2,000 by 2,000. Individual fibers for such an input/output arrangement are impractical, so ribbon fiber cable assemblies have been developed to address the greater density of inputs and outputs in these applications. These ribbon fiber arrangements require optical array connectors for interconnection to optical switches and other optical equipment within the network.
One such connector has been developed by the MT-RJ Alliance including the companies of Hewlett-Packard, Fujikura, AMP, Siecor, and USconec. The MT-RJ connector family utilizes an MT ferrule designed to hold 2, 4, 8, 12, or 16 fibers in a linear array. The MT ferrule is a precision molded solid part having tapered fiber receiving passageways which are loaded with a ribbon fiber array from a rear end. In line with the fiber array are a pair of pin receiving holes which are used to align the ferrule end faces of two mated ferrules. The pin holes must be precisely located with respect to the array of fiber receiving channels in order to insure proper alignment and minimize optical signal attenuation between mated fiber end faces. The ribbon is, secured into the ferrule with epoxy introduced through a transverse window formed in the ferrule. Once the epoxy is cured, the fibers are cleaved and polished at the front end or mating face to complete the ferrule and fiber array assembly. The ferrule and fiber array assembly may then be loaded into a variety of connector housings which are part of the MT-RJ or other connector systems.
It is important to maintain positional accuracy and alignment between the fiber array and pins so that upon mating with another ferrule, the end faces of the fibers are in alignment with each other to minimize coupling loss or attenuation at the interface. Unfortunately, since these ferrules are molded of plastic, they are not very stable and suffer from variation in material characteristics from one batch to another. Temperature history storage causes the positional accuracy of the optical fibers and pins to be compromised during storage and thermal cycling. Additionally, since these ferrules are designed to have tapered channels into which the fibers and epoxy are inserted, they must have sufficient clearance so that the fiber coated with epoxy will fit. This clearance results in some uncertainty as to where the fiber is located in relation to adjacent fibers in the array and in relation to the pins. This uncertainty results in a non-coaxial relationship between fiber cores in a mated pair of ferrules. Considering that the working core of a fiber is only a few microns in diameter, the positional tolerance is very small and large amounts of attenuation can be experienced with little positional uncertainty.
It is therefore an object of the present invention to provide a multi fiber ferrule having improved positional accuracy and reduced coupling loss, and to provide a tool and method for making the ferrule. It is further desirable to produce a new and improved multi part fiber ribbon cable connector whose outer dimensions make it a direct replacement for the MT ferrule requiring no modifications to the MT-RJ connector housing.
This and other objects are achieved by providing an array ferrule made from two halves. Each half may be cast or molded from ceramic, glass, plastic, or metal material. The halves are machined by a skiving or broaching method utilizing a broach tool. The broach has an exposed cutting edge for broaching the inner contour of each ferrule half. The ferrule halves are preferably identical having inner faces which are a mirror image of each other. The inner surfaces and channels are machined with the same tool, assuring coaxiality of mating fibers with an error only due to uncertainty of fiber core to fiber outer diameter relationship.